1. Field of the Invention
The present invention relates to a flat-type image display apparatus, and particularly to an image display comprising getter and a getter scattering preventive member.
1. Related Background Art
There have been known image display apparatuses such as those using liquid crystal, electron beam, EL (electro-luminescence), and of these the most commonly used image display apparatus for television is that employing the cathode-ray tube.
Television apparatuses using a cathode-ray tube generally have a disadvantage in that the depth of the apparatus is great in comparison to the size of the screen, thereby limiting the locations at which the television apparatus may be placed. Accordingly, in recent years, there has been research conducted on flat-type image display apparatuses which use electron beams, this arrangement requiring less depth of the apparatus than such employing the cathode-ray tube.
While flat-type image display apparatuses are smaller in volume than such employing cathode-ray tubes, the amount of gas emitted from the fluorescent material is great. Accordingly, a high level of skill is required to raise the degree of vacuum within the image display apparatus and further maintain that state.
Generally, in order to maintain the state within the sealed envelope at a high degree of vacuum, getter is employed. There are two types of getter; evaporation type, and non-evaporation type. With the evaporation type getter, the getter material is stored within an open container, following which this getter material is heated by means of conductive heating or electrical induction heating or the like, thus causing the getter material to evaporate (this process hereafter referred to as "flashing"), thereby causing the getter material to adhere to the interior of the envelope, consequently removing the gas from the airtight container. The non-evaporation type involves getter material being stored within an open container, following which the gas from is removed from the airtight container without causing flashing.
FIGS. 20A and 20B illustrate one example of the structure of a known vacuum fluorescent display tube as disclosed in Japanese Patent Publication No. 56-44534, with FIG. 20A being a plan view, and FIG. 20B being a cross-sectional view along the line denoted by 20B-20B in FIG. 20A.
As illustrated in FIG. 20B, this known example comprises a face plate 1601 composed of insulating material such as glass serving as an image display screen, and a rear plate 1602 set so as to oppose the face plate 1601. The area of contact between the face plate 1601 and the rear plate 1602 is sealed by means of glass with a low melting point, supersonic soldering, or resin which hardens in the presence of ultraviolet rays.
Further, a getter scattering prevention wall 1608 which doubles as a filament support is provided within this envelope so as to face the face plate 1601 and the rear plate 1602 in a generally vertical manner, and to this getter scattering prevention wall 1608, getter 1605 is fixed. Further, on the face plate 1601 situated on the other side of the getter scattering prevention member 1608 from the side provided with getter, a plurality of display units are arrayed, with each display unit comprising an image pattern 4, a control grid 1610 for controlling the content of the image, and a filament 1609. The getter scattering prevention wall 1608 is provided so that the getter material from the getter 1605 does not pass over to the image display unit side. Incidentally, reference numeral 9 in FIGS. 20A and 20B denotes a getter film, this formed by means of flashing of the getter 1605.
The image display apparatus constructed as described above is generally evacuated by means of connecting a turbo molecular pump or the like to an evacuation tube (not shown) and evacuating, and when the degree of vacuum within the envelope reaches a sufficient level, the evacuation tube is sealed by means of being stopped and severed, following which the getter 1605 is flashed, thus completing the image display apparatus.
After completion of the image display apparatus, heating the filament (thermionic cathode) 1609 causes electrons generated by means of the heating to be accelerated by means of an anode comprising an image pattern 4 (not shown), and strike fluorescent material (not shown) comprising an image pattern. Consequently, an image is displayed on the face plate 1601.
On the other hand, Japanese Laid-Open Patent Application No. 61-32336 mentions that with a flat-type image display apparatus, the amount of metal, glass, and ceramic comprising the electrode structure is several times that of a cathode-ray tube, whereas the area to which getter can be deposited to by flashing is less. Particularly, the inner wall area of the glass container is markedly smaller with a flat-type image display apparatus as compared to a cathode-ray tube. Accordingly, within the Japanese Laid-Open Patent Application No. 61-32336 is disclosed a fibrous shielding member such as steel wool or steel wool coated with graphite, for the purpose of increasing the area to which getter can be deposited by flashing, and preventing the getter subjected to flashing from passing over to the electrode structure or wires, causing short-circuiting between the electrodes or wires. This fibrous member is placed, for example, continuously or intermittently around the space formed between the inner wall of the glass container and the rear side of the electrode structure, i.e., the space where evaporation deposition of the getter is conducted, thus limiting the spread of the getter which attempts to pass over, and also increasing the area to which deposition of getter occurs by means of causing evaporation deposition of the getter to the surface of the shielding member.
However, known image display apparatuses constructed as described above have problems such as described below.
(1) Narrowing the distance between the outer edges of the getter scattering prevention wall and the outer frame, or increasing the density of the fibrous shielding material, as is done with known art, decrease the flowability of residual gas, i.e., the conductance thereof, to the getter flashing area within the envelope. In such an event, the capability of the getter may not be sufficiently exhibited, or modification in the brightness of the image may occur due to the pressure being uneven within the envelope. Further, this lengthens the amount of time required to evacuate the container via the evacuation tube.
(2) Widening the distance between the outer edges of the getter scattering prevention wall and the outer frame, or decreasing the density of the fibrous shielding material improves the conductance, but the getter material may pass over to the image display portion via the gap between the getter scattering prevention wall and the outer frame or via the gaps in the fibrous shielding material, thus adhering to the electron emission source or fluorescent material, and possibly causing short-circuiting of the wiring.
(3) Further, in the case of flat-type image display apparatuses, the area occupied by the electron emission source and the area occupied by the fluorescent material are often approximately the same, and moreover, the distance between the electron emission source and the fluorescent material corresponding to the depth of the CRT is around several hundred .mu.m to several tens of mm.
Accordingly, the area capable of placement of getter within the flat-type image display apparatus is markedly reduced compared to that of the CRT, although the area of getter adhesion required therein is equal to or greater than that of the CRT, due to the degree of vacuum required being equal to or greater than that of the CRT. Consequently, it becomes important to secure area for placement of getter therein, increasing the amount of getter placed, and also preventing the aforementioned getter from passing over.